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.Dd August 31, 2023
.Dt UEFI 8
.Os
.Sh NAME
.Nm UEFI
.Nd Unified Extensible Firmware Interface bootstrapping procedures
.Sh DESCRIPTION
The
.Nm
Unified Extensible Firmware Interface provides boot- and run-time services
to operating systems.
.Nm
is a replacement for the legacy BIOS on the i386 and amd64 CPU architectures,
and is also used on arm, arm64 and riscv architectures.
.Pp
The UEFI specification is the successor to the Extensible Firmware Interface
(EFI) specification.
The terms UEFI and EFI are often used interchangeably.
.Pp
The
.Nm
boot process loads system bootstrap code located in an EFI System Partition
(ESP).
The ESP is a GPT or MBR partition with a specific identifier that contains an
.Xr msdosfs 4
FAT file system with a specified file hierarchy.
.Bl -column -offset indent "Partition Scheme" "ESP Identifier"
.It Sy "Partition Scheme" Ta Sy "ESP Identifier"
.It GPT Ta C12A7328-F81F-11D2-BA4B-00A0C93EC93B
.It MBR Ta 0xEF
.El
.Pp
The
.Nm
boot process proceeds as follows:
.Bl -enum -offset indent -compact
.It
.Nm
firmware runs at power up and searches for an OS loader in the EFI system
partition.
The path to the loader may be set by an EFI environment variable managed by
.Xr efibootmgr 8 .
If not set, an architecture-specific default is used.
.Bl -column -offset indent "Architecture" "Default Path"
.It Sy Architecture Ta Sy Default Path
.It amd64 Ta Pa /EFI/BOOT/BOOTX64.EFI
.It arm Ta Pa /EFI/BOOT/BOOTARM.EFI
.It arm64 Ta Pa /EFI/BOOT/BOOTAA64.EFI
.It i386 Ta Pa /EFI/BOOT/BOOTIA32.EFI
.It riscv Ta Pa /EFI/BOOT/BOOTRISCV64.EFI
.El
.Pp
The default
.Nm
boot configuration for
.Fx
installs
.Pa loader.efi
in the default path.
.It
.Pa loader.efi
reads boot configuration from
.Pa /boot.config
or
.Pa /boot/config .
.It
.Pa loader.efi
loads and boots the kernel, as described in
.Xr loader.efi 8 .
.El
.Pp
The
.Xr vt 4
system console is automatically selected when booting via
.Nm .
.Sh FILES
.Bl -tag -width /boot/loader -compact
.Nm
bootstrap
.It Pa /boot/loader.efi
Final stage bootstrap
.It Pa /boot/kernel/kernel
Default kernel
.It Pa /boot/kernel.old/kernel
Typical non-default kernel (optional)
.El
.Sh SEE ALSO
.Xr msdosfs 4 ,
.Xr vt 4 ,
.Xr boot.config 5 ,
.Xr boot 8 ,
.Xr efibootmgr 8 ,
.Xr efidp 8 ,
.Xr efivar 8 ,
.Xr gpart 8 ,
.Xr loader.efi 8 ,
.Xr uefisign 8
.Sh HISTORY
EFI boot support for the ia64 architecture first appeared in
.Fx 5.0 .
.Nm
boot support for amd64 first appeared in
.Fx 10.1 ;
for arm64 in
.Fx 11.0 ;
for armv7 in
.Fx 12.0 ;
and for riscv in
.Fx 13.0 .
.Sh BUGS
There is no support for 32-bit i386 booting via UEFI.
